An ECG (electrocardiogram) system is a widely applied medical examination and monitoring instrument that produces an electrocardiogram (ECG) waveform. A typical ECG waveform includes a series of characteristic points designated by the letters P, Q, R, S, and T. The Q, R, and S portions of the wave when taken together are referred to as a “QRS complex”. The R-wave of the QRS complex is the most prominent portion in each cardiac cycle of an ECG signal. In various ECG applications, it is crucial for the ECG system to accurately determine the timing of R-wave peaks.
A conventional ECG system includes an analog frontend circuit, an ADC and a digital signal processor to carry out the task of determining R-wave peaks. Typically, the ADC and the digital signal processor consume a great amount of power, which is often many times of the power consumed by the analog frontend circuit. Relatively large power consumption and considerable complexity of the circuit makes such an ECG system not suitable to be worn by a user so as to constantly examine and monitor heart conditions of the user.
On the other hand, to reduce system power consumption, the ADC and the digital signal processor are eliminated in some wearable ECG systems, so that the determination of ECG are solely relied on pure analog circuits. However, when there are a lot of noises present in the signal acquired by the ECG system, for example, when the person being tested is in motion, it is difficult for pure analog circuits to accurately determine ECG, which therefore greatly limits the application scenarios of such wearable ECG systems.